the manufacture of aluminum by electrolysis of bauxite started, and the price for pure aluminium

Chemical structure of bortzemib
KAl(SO4)2⋅12H2O), which was used for medicinal purposes in Roman times. Initially, it was very difficult
to prepare pure aluminium and therefore it was regarded as a very precious substance. In the mid-1800s,
aluminium cutlery was used for elegant dinners, whereas it is nowadays used as lightweight camping cutlery.
In 1886, the manufacture of aluminium by electrolysis of bauxite started, and the price for pure aluminium
dropped significantly. Aluminium is a soft, durable and lightweight metal, which makes it attractive to many
applications. Nowadays, aluminium is mainly used for the construction of cars and aircrafts and can be found
in packaging and construction materials.
4.3.2 Biological importance
The human body contains around 35 mg of Al3+, of which ∼50% is found in the lungs and ∼50% in the
skeleton. There is no known biological role for Al3+ and, indeed, the human body has developed very effective
barriers to exclude it. Only a minimal fraction of Al3+ is taken up from the diet in the gut, and the kidneys
fairly quickly excrete most of it. The bones can act as a sink for Al3+ if the blood concentration is high and
release it slowly over a long period. The brain is vulnerable to Al3+ and usually the blood–brain barrier
prevents Al3+ entering the brain. Al3+ can sometimes act as a competitive inhibitor of essential elements
such as Mg2+, Ca2+ and Fe2+/3+ because of their similar ionic radii and charges. It is important to note that at
physiological pH, Al3+ forms a barely soluble precipitate Al(OH)3, which can be dissolved by changing the
pH (see Equations 4.8 and 4.9) [6].
A normal adult diet contains typically between 2.5 mg/day and up to 13 mg/day Al3+, but patients
on aluminium-containing medication can be exposed to more than 1000 mg/day. Typically, ∼0.001% is
absorbed in the digestive tract, but it can be around 0.1–1.0% when it is in the form of aluminium citrate
(Figure 4.5) [6b].
Al3+ can accumulate in the human body if natural limits are crossed, for example, intravenous administration or patients on dialysis, or when the kidneys are impaired and therefore not able to excrete Al3+
sufficiently. Under normal circumstances, Al3+ would not accumulate in the human body. Nevertheless, in
1972, Alfrey et al. described the new syndrome of progressive dialysis encephalopathy, the so-called dialysis
dementia, which was seen in patients being treated with haemodialysis for 15 months or more. The symptoms
include speech disorders, problems with the bone mineralisation and general signs of dementia. Investigations
showed that brain scans were normal and that there was no connection to the Alzheimer’s disease, as neither
neurofibrillary tangles nor senile plaques were found. Increased serum and bone concentrations of Al3+ were
The Boron Group – Group 13 73
O
AI
O
O
OH O
O
O
Figure 4.5 Chemical structure of aluminium citrate
found in patients who were on haemodialysis, and the connection was made to the toxicity of the Al3+ present
in the dialysate solution. Nowadays, the use of modern Al3+-free dialysate solutions or new techniques (e.g.
reverse osmosis) prevents ‘dialysis dementia’ [6a].
4.3.3 Al3+ and its use in water purification
Al3+ is used in the purification of water. Lime (CaO) and aluminium sulfate Al2(SO4)3 are added to waste
water in order to accelerate the settling or sedimentation of suspended matter [7]. The addition of lime
increases the pH of the water slightly (Equation 4.10). The water becomes more basic, which promotes the
precipitation of Al3+ as Al(OH)3 (Equation 4.11).
CaO(s) + H2O(l) → Ca2+
(aq) + 2OH−
(aq) (4.10)
Al3+
(aq) + 3OH−
(aq) → Al(OH)3(s) (4.11)
Al(OH)3 precipitates as a gelatinous precipitate which slowly settles. During this process, it incorporates
suspended soil, colloidal material and most bacteria. The water is filtered before leaving the treatment plant
in order to remove the flocculate and the vast majority of the Al3+. WHO guidelines allow a maximum concentration for Al3+ of 0.2 mg/l [8].
4.3.4 Aluminium-based adjuvants
An adjuvant is an agent or a mixture of agents that possesses the ability to bind to a specific antigen. Adjuvants are added to vaccines in order to increase the antibody responses to the vaccination and/or to stabilise
the preparation. Adjuvants can absorb many antigenic molecules over a wide surface area, thus enhancing the
interaction of immune cells with the presenting antigens and leading to an increase of the immune response
stimulation. Some adjuvants (including aluminium-based ones) can function as a slow-release delivery system. They trap the antigen in a depot created by the adjuvant at the injection site. From there, the antigen is
slowly released, which causes a steady stimulation of the immune system.
Aluminium-based adjuvants have a long-standing tradition and have been used for more than 50 years.
They are the most widely used adjuvants in human and veterinary vaccines and regarded as safe if applied
correctly. Al3+ salts are the only kind of adjuvant licensed by the FDA. They are also the only kind of adjuvants used in anthrax vaccines for humans in the United States. Anthrax vaccine contains Al(OH)3, as do the
FDA-licensed diphtheria, haemophilus influenzae type B, hepatitis A, hepatitis B, Lyme disease, pertussis
and tetanus vaccines. In many countries, vaccines for children contain aluminium-based adjuvants [9].
The adjuvant effect of potassium alum (KAl(SO4)2⋅12H2O) was first discovered in 1926. Researchers
examined diphtheria toxoids precipitated with alum and were able to show that an injection of this alum
precipitate led to a significant increase in immune response. Leading on from this research, alum has found
74 Essentials of Inorganic Chemistry
widespread use as an adjuvant. Vaccines containing alum as adjuvant are referred to as alum-precipitated
vaccines. Unfortunately, it has been shown that alum precipitations can be highly heterogeneous. The homogeneity of the preparation depends on the anions and the conditions present at the point of precipitation [9].
Subsequent research showed that aluminium hydroxide (Al(OH)3) hydrogels can be pre-formed in a standardised manner and be used to absorb protein antigens to form a homologous preparation. Following on
from this research, researchers have shown that it is possible to co-precipitate aluminium phosphate (AlPO4)
and the diphtheria toxoid in order to form active vaccines. These vaccines are called aluminium-absorbed
vaccines and, in contrast to alum-precipitated vaccines, the antigens are distributed homogeneously. Nowadays, aluminium-absorbed vaccines have taken over from alum-precipitated ones. Nevertheless, there is a lot
of ambiguity found in the literature, where both terms are interchangeably used [9].
In summary, immunisation vaccines containing adjuvants are more effective than those without them. Typical adjuvants are alum [KAl(SO4)2⋅12H2O], Al(OH)3, AlPO4, Al2O3, but oxides of other metals, such as
ZrO2, SiO2 and Fe2O3, are also under investigation.
The formation of the aluminium hydrogels is generally achieved by reacting Al3+ ions (from compound
such as AlCl3) under alkaline aqueous conditions. Conditions are strongly regulated, as even smallest changes
to parameters such as temperature, concentration and others can influence the quality of the hydrogel. Aluminium phosphate gels are typically produced by reacting Al3+ salts in the presence of phosphate ions under
alkaline conditions [9].
The mode of action is highly complex and still not fully understood. Initial theories included the physical
absorption of the antigen, which is still considered as an important feature, and the gradual release of antigen
from the injection side with the adjuvant working as an agglomeration. The latter theory was disproved
quickly. Research has shown that antigens need to be adsorbed to the adjuvant before the immunisation
reaction. It is believed that the adjuvant will then present the antigen to the immunocomponent of the targeted
cell [9].
4.3.5 Antacids
The function of antacids is to neutralise excess stomach acid. They also exhibit cytoprotective effects towards
attacks against the gastric mucosa. They are additionally known to heal gastric and duodenal ulcerations;
nevertheless, the mechanism is still uncertain.
Antacids have been in use for the past 2000 years, and the initial formulations were based on CaCO3 (coral
and limestone). Nowadays, the antacid/anti-gas market is a significant income stream for the pharmaceutical
industry and the demand for antacids is expected to grow. The number of people suffering from heartburn
increases with an ageing population, more stressful lifestyles and changing eating habits such as eating out
more often.
Aluminium hydroxide (Al(OH)3) has several medical applications. It is used as an antacid for treating
heartburn as well as acid indigestion (reflux oesophagitis). It is also known to have healing properties of
peptic ulcers. In patients suffering from kidney failure, who show elevated serum phosphate levels (hyperphosphataemia), Al(OH)3 is used as a phosphate binder (see Section 4.3.7).
Al(OH)3 is an amphoteric compound (see Section 4.1.2.2), which means it can react as a base or as an
acid. In its application as an anti-acid, Al(OH)3 reacts with any excess stomach acid (mainly HCl) with the
formation of AlCl3 and water (Equation 4.12).
Al(OH)3 + 3HCl → AlCl3 + 3H2O (4.12)
Al(OH)3 is known to cause constipation, so formulations of anti-acids often include a combination with
Mg2+ antacids. Usually, oral antifoaming agents, such as simethicone, are added in order to reduce bloating
The Boron Group – Group 13 75
Table 4.2 Typical formulation of an antacid/antigas
mixture (maximum strength Maalox®, Max®, Norvatis)
Active ingredient Quantity (mg) Purpose
Al(OH)3 400 Antacid
Mg(OH)2 400 Antacid
Simethicone 40 Anti-gas
HO O
AI
OH O
NH2

which term refers to the refining of aluminum by electrolysis
extraction of aluminum by electrolysis
aluminum is extracted from alumina by electrolysis of a molten mixture of
aluminum is produced commercially by the electrolysis of al2o3
why does aluminum have to be extracted by electrolysis
in the extraction of aluminum from alumina by electrolysis cryolite is added to
describe the process of preparation of aluminum by the electrolysis of alumina
aluminum is obtained by the electrolysis of pure dissolved in
2.describe the process of preparation of aluminum by the electrolysis of alumina
aluminum extraction by electrolysis
aluminum is extracted from alumina by electrolysis
the compound from which aluminum is obtained by electrolysis in british columbia is
making aluminum oxide by electrolysis

You May Also Like